In recent years, nonaqueous electrolyte batteries, in which materials having the capability of absorbing and releasing lithium ions are used as a positive active material and a negative active material, are used in various applications such as power supplies for electric vehicles, power-assisted bicycles, UPS (uninterruptible power supply), and mobile devices such as mobile phones, notebook computers and smart phones. Also, the application of an electrical energy storage system, which uses a nonaqueous electrolyte battery in combination with a solar power or a wind power, etc., has been rapidly grown for the purpose of handling a recently increased concern about environmental problems such as global warming and large-scale disasters.
In these extensively broadened applications, the specifications required for batteries are different from those of conventional mobile devices. In the application of electrical energy storage, easy maintenance and a long service life are required in addition to high safety, high energy density (reduction in size and weight) and a low cost. Therefore, it is necessary to achieve the refinements to prevent nonaqueous electrolyte solutions from leaking to the outside of a nonaqueous electrolyte battery and to prevent moisture penetrating from the outside of a battery from deteriorating nonaqueous electrolytes.
By the way, as an exterior package for housing a positive electrode and a negative electrode, a member made of a film material is widely used instead of a conventional metallic can in order to achieve the further reductions in thickness and weight. Examples of a film material include a composite film in which an external impact protection film represented by a nylon film is prepared as an outermost layer, a metallic layer for moisture prevention and light shielding represented by an aluminum foil is prepared as an intermediate layer, and a thermally adhesive resin film for sealing an electrode group and electrolyte solutions is prepared as an innermost layer.
Known examples of an exterior package formed of a film material include the exterior package including the rectangular molded part (the rectangular cup part) produced by a deep drawing process, the four peripheral parts extending from the four sides of the cup part in horizontal directions, and the flat plate part connected to one of these peripheral parts. The cup part of the exterior package houses the positive electrode and negative electrode having the capability of absorbing and releasing lithium ions and the electrode group which has a lithium ion-conducting solid electrolyte layer or a separator interposed between the positive electrode and the negative electrode.
The terminals connected to the respective positive electrode and negative electrode of the electrode group extend to the outside along one or two peripheral parts except for the peripheral part connected to the flat plate part of the exterior package. Also, this exterior package is arranged such that the thermally adhesive resin films of the film materials on the cup part side and the flat plate part side face each other when the flat plate part of the exterior package is bent on the axis of the peripheral part toward the cup part at an angle of 180°. The thermoplastic insulating films having a metallic adhesion property are provided between the extended parts of the terminals and the thermally adhesive resin films of the flat plate part. Alternatively, the thermoplastic insulating films having a metallic adhesion property are preliminarily provided at the thermally adhesive parts of the terminals. When the flat plate part of the exterior package is bent at an angle of 180° and the three peripheral parts are heat-sealed except for the peripheral part connected to the flat plate part, the aforementioned electrode group is airtightly housed in the aforementioned exterior package.